I think that Ammo and Hammer are different players so it's hard to do a straight up comparison. Hammer provides a valuable asset in being a catch and shoot scorer whereas Ammo didn't really accel in doing that. What's really the downside in having both is neither is good defensively.
Couple points in Hammer's favor though: 1) Vincent giving him sporadic PT is a decent excuse for his struggles this year. 2) His contract is frontloaded. We might be paying retail now but in a couple of years he'll be well worth his money and will be a good asset.